Method for manufacturing semiconductor device

ABSTRACT

A method for manufacturing a semiconductor device having steps of forming an amorphous semiconductor on a substrate having an insulating surface; patterning the amorphous semiconductor to form plural first island-like semiconductors; irradiating a linearly condensed laser beam on the plural first island-like semiconductors while relatively scanning the substrate, thus crystallizing the plural first island-like semiconductors; patterning the plural first island-like semiconductors that have been crystallized to form plural second island-like semiconductors; forming plural transistors using the plural second island-like semiconductors; and forming a unit circuit using a predetermined number of the transistors, where the second island-like semiconductors used for the predetermined number of the transistors are formed from the first island-like semiconductors that are different from each other.

This invention relates to a semiconductor device and a method forpreparing the same.

DESCRIPTION OF THE RELATED ART

Recently, a technique has been broadly used in which an amorphoussemiconductor layer formed on an insulating material such as a glasssubstrate is crystallized to provide a crystalline semiconductor layerand a thin film transistor (hereinafter referred to as TFT) using thecrystalline semiconductor layer as an active layer is formed. Itselectrical property has been significantly improved.

As a result, a signal processing circuit, which was externally mountedusing an IC or the like in the conventional technique, can be formedusing a TFT, and a display device in which a pixel part and a drivingcircuit are integrally formed on a substrate is realized. Since thesmall size and light weight of the display device because of reductionin number of components enable significant reduction in manufacturingcost, a broad range of research and development on the display devicehas been recently carried out.

BRIEF SUMMARY OF THE INVENTION

There are cases in which electrical properties are different even ifTFTs having the same size are fabricated when TFTs are fabricated usingpolysilicon.

Typical circuits formed using transistors are operational amplifiers anddifferential amplifiers. FIG. 10A shows a current mirror circuit. FIG.10B shows an exemplary layout of the current mirror circuit on an actualsubstrate. FIG. 10C shows a differential amplifier. FIG. 10D shows anexemplary layout of the differential amplifier on an actual substrate.

As shown in FIG. 10A, the current mirror circuit has two transistors. Adrain current I₁ flowing through a transistor 201 and a drain current I₂flowing through a transistor 202 need be equal. That is, the currentmirror circuit operates on the assumption that the transistor 201 andthe transistor 202 have the same property. As a result, if theelectrical properties of the two transistors are not equal, I₁=I₂ cannotnecessarily be achieved and therefore the current mirror circuit doesnot function as a circuit. Therefore, in most cases, transistorsconstituting a current mirror circuit have equal channel length, channelwidth and the like.

Next, as shown in FIG. 10C, the differential amplifier has a currentmirror circuit as an active load. This differential amplifier is acircuit such that a waveform formed by amplifying the potentialdifference between signals inputted to In₁ and In₂ can be taken out froman output terminal (Out), utilizing I₁=I₂+I₃ realized by the currentmirror circuit when different electric potentials are supplied to inputterminals (In₁, In₂). This circuit, too, operates on the assumption thatTFTs 221 to 214 have the same electric property.

In short, in the current mirror circuit shown in FIGS. 10A and 10B andthe differential amplifier shown in FIGS. 10C and 10D, the pluralconstituent TFTs must have device consistency. Actually, however, ap-SiTFT is formed by concentrating many crystal grains in asemiconductor layer and its electrical property is degraded because thecrystal grains have different orientations on the grain boundariesthough each of the crystal grains has a good crystal state. That is, ap-Si TFT has many such crystal grains contained in the active layer, andthe difference in number of crystal grains and the difference inorientation between adjacent crystal grains may cause difference inelectric property. Even if TFTs of the same size are manufactured andthe same voltage is applied to their electrodes, the current values maydiffer.

In view of the foregoing status of the art, it is an object of thepresent invention to provide a method for manufacturing a semiconductordevice which restrains the influence of difference in electric propertybetween circuits requiring consistency of plural TFTs as in theabove-described current mirror circuit.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIGS. 1A–1C are views for explaining an embodiment mode of the presentinvention in which grapho-epitaxy is used.

FIGS. 2A–2B are views for explaining an embodiment mode of the presentinvention in which grapho-epitaxy is used.

FIGS. 3A–3B are views for explaining an embodiment mode of the presentinvention.

FIGS. 4A–4B are views for explaining an embodiment mode of the presentinvention.

FIGS. 5A–5F are views for explaining an embodiment mode of the presentinvention.

FIG. 6 is a view for explaining an embodiment mode of the presentinvention.

FIG. 7 is a view for explaining an embodiment mode of the presentinvention.

FIG. 8 is a view for explaining an embodiment mode of the presentinvention.

FIG. 9 is a view for explaining an embodiment mode of the presentinvention.

FIGS. 10A–10D are views showing a current mirror circuit and adifferential amplifier.

FIGS. 11A–11B are views for explaining laser irradiation on asemiconductor layer.

FIGS. 12A–12B are views for explaining a laser irradiation device.

FIGS. 13A–13I are views for explaining an irradiation range of the laserirradiation device.

FIGS. 14A–14B are views for explaining a laser irradiation device.

FIGS. 15A–15B are views for explaining a laser irradiation on asemiconductor layer.

FIGS. 16A–16B are views for explaining process flows includingcrystallization by laser irradiation on a semiconductor layer.

FIGS. 17A–17B are views for explaining process flows includingcrystallization by laser irradiation on a semiconductor layer.

FIGS. 18A–18E are views for explaining a process for preparing asemiconductor device.

FIGS. 19A–19F are views for explaining a process for preparing asemiconductor device.

FIGS. 20A–20E are views for explaining a process for preparing asemiconductor device.

FIG. 21 is a view for explaining a process for preparing a semiconductordevice.

FIGS. 22A–22B are views for explaining a process for preparing asemiconductor device.

FIGS. 23A–23C are views for explaining a process for preparing asemiconductor device.

FIGS. 24A–24B are views for explaining a process for preparing asemiconductor device.

FIGS. 25A–25E are views for explaining a process for preparing asemiconductor device.

FIGS. 26A–26C are views for explaining a process for preparing asemiconductor device.

DETAILED DESCRIPTION OF THE INVENTION

In view of the foregoing object, the present invention provides thefollowing measures.

A method for manufacturing a semiconductor device according to thepresent invention comprises:

forming an amorphous semiconductor on a substrate having an insulatingsurface;

patterning said amorphous semiconductor into a desired shape to formplural first island-like semiconductors;

irradiating a linearly condensed laser beam on the plural firstisland-like semiconductors while relatively scanning the substrate, thuscrystallizing the plural first island-like semiconductors;

patterning the plural first island-like semiconductors that have beencrystallized into a desired shape to form plural second island-likesemiconductors;

forming plural transistors using the plural second island-likesemiconductors; and

forming a unit circuit using a predetermined number of the transistors,of the plural transistors;

wherein the second island-like semiconductors used for the predeterminednumber of the transistors are formed from the first island-likesemiconductors that are different from each other.

Another method for producing a semiconductor device according to thepresent invention comprises:

forming an amorphous semiconductor on a substrate having an insulatingsurface;

forming a metal-containing layer on the amorphous semiconductor andforming a first crystalline semiconductor by heat treatment;

patterning the first crystalline semiconductor into a desired shape toform plural first island-like semiconductors;

irradiating a linearly condensed laser beam on the plural firstisland-like semiconductors while relatively scanning the substrate, thusforming the plural first island-like semiconductors containing secondcrystalline semiconductors;

patterning the first island-like semiconductors containing the secondcrystalline semiconductors into a desired shape to form plural secondisland-like semiconductors;

forming plural transistors using the plural second island-likesemiconductors; and

forming a unit circuit using a predetermined number of the transistors,of the plural transistors;

wherein the second island-like semiconductors used for the predeterminednumber of the transistors are formed from the first island-likesemiconductors that are different from each other.

With the above-described structure, the present invention can equalizethe properties of unit circuits and therefore can restrain the influenceof difference in property of TFTs.

EMBODIMENT MODES OF THE INVENTION

Embodiment Mode 1

An embodiment mode of the present invention will now be described withreference to FIGS. 3 to 5. FIGS. 3 to 5 show a method for preparing asemiconductor device according to the present invention. In FIGS. 3A and3B and FIGS. 4A and 4B, oblique views are shown on the left side and topviews are shown on the right side. FIGS. 5A to 5F simply show the methodfor preparing a semiconductor device according to the present invention.

A semiconductor 102 is formed on a substrate 101 (FIG. 3A). As thesubstrate 101, any material that is durable to the processingtemperature throughout the manufacture of a semiconductor device may beused. For example, a quartz substrate, a silicon substrate, anon-alkaline glass substrate containing barium borosilicate glass oraluminoborosilicate glass or the like, or a substrate having aninsulating film formed on a surface of a metal substrate can be used.Also a plastic substrate that is heat-resistant enough to be durable tothe processing temperature may be used.

Between the substrate 101 and the semiconductor 102, an base film forpreventing contamination of the semiconductor 102 due to impurity suchas alkaline metal contained in the substrate 101 may be formed using aninsulating film or the like. The semiconductor 102 may be depositedusing a known technique (sputtering, LPCVD, or plasma CVD). Thesemiconductor 102 may be an amorphous semiconductor or may be amicrocrystalline or polycrystalline semiconductor.

Next, the semiconductor 102 is patterned to form an alignment marker 103and first island-like semiconductors 104 (FIG. 3B). In the presentinvention, plural first island-like semiconductors 104 are arranged inparallel on the substrate 101. The first island-like semiconductor 104has one or plural sharp pointed end parts. A laser beam is caused toscan from the one or plural pointed end parts to the other end part onthe opposite side. That is, in the first island-like semiconductor 104,a laser beam first reaches the pointed end part. In this embodimentmode, the pointed end part is referred to as a-point. In the presentinvention, the plural first island-like semiconductors are arranged inparallel in the longitudinal direction. In the lateral direction, theplural first island-like semiconductors are slightly shifted from eachother so that the pointed end parts (a-points) of the first island-likesemiconductors are not aligned with each other (FIG. 3B). The alignmentmarker 103 and the first island-like semiconductors 104 are not limitedto the shapes shown in FIG. 3B.

Next, as shown in FIG. 4A, a laser irradiating position is decided onthe basis of the alignment marker 103 and a laser beam 106 is irradiatedon the first island-like semiconductors 104, thereby crystallizing thefirst island-like semiconductors 104. In the case where thesemiconductors forming the first island-like semiconductors have beencrystallized to a certain extent, the crystallinity is further increasedby this laser irradiating step. In this case, a slit (not shown) coversan area having a low energy density of the laser beam, thus preventingirradiation of the semiconductors with the laser beam in this area. If alaser beam with a low energy density is irradiated on and crystallizesthe semiconductor, the resulting crystal grains are microcrystal grainsof approximately 0.1 μm or less and such a crystalline semiconductorcannot provide an excellent electrical property. Whether the energydensity is enough or not is judged on the basis of whether desiredcrystal grains can be obtained or not in the semiconductor. A designermay properly judge this. Therefore, if the designer judges that thecrystallinity is not enough, it is judged that the energy density islow.

Since the energy density of the laser beam is lowered near an end partof a laser beam spot obtained through the slit, crystal grains becomesmaller near an end part of irradiating and a protruding part (ridge)appears along the crystal grain boundary. Therefore, the trajectory ofthe laser beam spot (indicated by dotted lines in FIG. 4A) and the firstisland-like semiconductors 104 are arranged so as not to overlap eachother. At least, areas of second island-like semiconductors (indicatedby dotted lines in the first island-like semiconductors 104 in FIG. 4A),which will be formed later from the first island-like semiconductors104, are arranged so as not to overlap the trajectory of the laser beamspot.

When irradiating the laser beam on the first island-like semiconductors,the scanning direction of the laser beam or the shape of the firstisland-like semiconductors is decided so that when the laser beam spotreaches the end part of the first island-like semiconductor, the laserbeam spot and the first island-like semiconductor contact each other atone point, as viewed from the front or back side of the substrate. InFIG. 4A, each of the first island-like semiconductors 104 first contactsthe laser beam spot at its pointed end part (a-point). As irradiationwith the laser beam is started at one contact point in this manner andthe semiconductor is thus crystallized, a crystal having a (100)orientational plane grows from the vicinity of the contact pointincluding this contact point. Therefore, finally, the rate of the (100)orientational plane is increased in the first island-likesemiconductors. That is, since the crystal grains have uniformorientational planes, electrons or holes smoothly migrate near the grainboundary. Such crystalline semiconductors have very high field-effectmobility.

In the present invention, plural second island-like semiconductors areformed from the first island-like semiconductors 104. In thisspecification, for example, it is assumed that three second island-likesemiconductors 105 are formed from each of the first island-likesemiconductors 104 shown in FIGS. 3 and 4. The three second island-likesemiconductors 105 are referred to, from the side of the pointed endpart (a-point), as second island-like semiconductor A, secondisland-like semiconductor B, and second island-like semiconductor C.Then, since crystallization starts at the pointed end part (a-point) ofthe first island-like semiconductor 104, the crystallinity of the secondisland-like semiconductors A to C differs. In other words, the electricproperties of the second island-like semiconductors depend on thedistance from the pointed end part (a-point). Thus, in the presentinvention, the following measure is taken to restrain the difference inproperty of the circuit constituted by the second island-likesemiconductors A to C.

In the present invention, the plural first island-like semiconductorsare arranged in parallel in the longitudinal direction. In the lateraldirection, the first island-like semiconductors are slightly shiftedfrom each other so that the a-points of the first island-likesemiconductors are not aligned with each other. In the presentinvention, a unit circuit is formed using three different secondisland-like semiconductors formed from three different first island-likesemiconductors. In this case, of the three first island-likesemiconductors, a part corresponding to the second island-likesemiconductor A from one first island-like semiconductor, a partcorresponding to the second island-like semiconductor B from anotherfirst island-like semiconductor, and a part corresponding to the secondisland-like semiconductor C from the other first island-likesemiconductor are arranged to be aligned with each other in the lateraldirection.

In this specification, a unit circuit means a circuit in which pluraltransistors are electrically connected with each other. Typically, it isa circuit in which plural transistors are connected in parallel and areelectrically connected with each other. For example, an analog switch, acurrent source, a current mirror circuit, a differential amplifier, anoperational amplifier circuit and the like are equivalent to unitcircuits.

Next, as shown in FIG. 4B, the crystallized first island-likesemiconductors 104 are patterned to form the second island-likesemiconductors 105 of a desired shape. It is desired that the secondisland-like semiconductors 105 use areas near the center of the firstisland-like semiconductors 104 where good crystallinity is providedwhile avoiding areas near the end parts of the first island-likesemiconductors 104. The marker 103 may be maintained so that it can beused for aligning a mask in later steps (forming of gate electrodes,forming of wirings and the like).

In the present invention, a unit circuit is formed using a partcorresponding to the second island-like semiconductor A from one firstisland-like semiconductor, a part corresponding to the secondisland-like semiconductor B from another first island-likesemiconductor, and a part corresponding to the second island-likesemiconductor C from the other first island-like semiconductor, of thethree first island-like semiconductors 104.

In the present invention, plural second island-like semiconductorsconstituting a unit circuit are formed from different first island-likesemiconductors. When a unit circuit is formed using three secondisland-like semiconductors, the three second island-like semiconductorsare set to have different distances from the pointed end part (a-point).By so setting, the different properties of the second island-likesemiconductors can be averaged. As a result, the properties of unitcircuits can be equalized.

FIGS. 5A to 5D simply show the foregoing process. In the presentinvention, plural second island-like semiconductors 306 are formed froma first island-like semiconductor 302. However, FIGS. 5A to 5D show thecase where one second island-like semiconductor 306 is formed from thefirst island-like semiconductor 302, for simplification.

A gate electrode 307 and source and drain wirings 308, 309 are formed onthe second island-like semiconductor 306, thus forming a TFT. FIG. 5F isa sectional view along a line A–A′ in FIG. 5E.

In the present invention, a known laser can be used as a laser forirradiating the semiconductor. The laser may be a pulse-oscillating orcontinuously oscillating gas laser or solid laser. As the gas laser, anexcimer laser, an Ar laser, a Kr laser or the like may be used. As thesolid laser, a YAG laser, a YVO₄ laser, a YLF laser, a YAlO₃ laser, aglass laser, a ruby laser, an alexandrite laser, a Ti:sapphire laser orthe like may be used. Moreover, as a solid laser, a laser using crystalsof YAG, YVO₄, YLF, a YAlO₃ or the like doped with Cr, Nd, Er, Ho, Ce,Co, Ni or Tm may be employed. The fundamental wave of the laser variesdepending on the material to dope with, and a laser beam with afundamental wave of approximately 1 μm is obtained. The harmonic withrespect to the fundamental wave is obtained by using a non-linearoptical element. Moreover, an ultraviolet laser beam obtained by anon-linear optical element from a green laser beam, which is convertedby another non-linear optical element from an infrared laser beamemitted from a solid laser, can be used.

In the present invention, the width of the beam spot can be properlychanged in accordance with the size of the first island-likesemiconductor or the second island-like semiconductor. For example, aTFT of a driving circuit in which flow of a relative large quantity ofcurrent is desired has a large channel width and therefore the size ofthe second island-like semiconductor tends to be large, compared with apixel part. Thus, the case of scanning the first island-likesemiconductors of two sizes with a laser beam while changing the widthof the slit will now be described with reference to FIG. 11.

FIG. 11A shows the relation between a part scanned with a laser beam andthe first island-like semiconductor in the case where the firstisland-like semiconductor has a short length in the directionperpendicular to the scanning direction. FIG. 11B shows the relationbetween a part scanned with a laser beam and the first island-likesemiconductor in the case where the first island-like semiconductor hasa long length in the direction perpendicular to the scanning direction.

If the width of a spot 1901 in FIG. 11A is W₁ and the width of a spot1902 in FIG. 11B is W₂, W₁<W₂ holds. Of course, the width of the spot isnot limited to these, and if there is an enough spacing between thefirst island-like semiconductors in the direction perpendicular to thescanning direction, the width can be freely set.

In the present invention, as shown in FIGS. 11A and 11B, scanning withthe spot is carried out so that at least the first island-likesemiconductor parts are crystallized, instead of irradiating the laserbeam on the entire surface of the substrate. Since the laser beam is notirradiated on the entire surface of the substrate but it is irradiatedon the minimum necessary parts to enable crystallization of the firstisland-like semiconductors, the processing time required for onesubstrate can be suppressed and the efficiency of substrate processingcan be improved.

(Embodiment Mode 2)

In this embodiment mode, as a different embodiment mode from EmbodimentMode 1, a method for preparing a semiconductor device to which theprinciple of grapho-epitaxy is applied will be described with referenceto FIGS. 1 and 2.

The basic principle of grapho-epitaxy utilizes the anisotropy of surfaceenergy held by crystals to be grown. The anisotropy of surface energymeans a characteristic such that, for example, crystals of salt grownfrom a solution exhibit regular hexahedrons. In the case of an SOIstructure, it means the anisotropy of surface energy between SiO₂ andSi.

In FIG. 1A, 10 represents a substrate. As the substrate 10, any materialthat is durable to the processing temperature throughout the manufactureof a semiconductor device may be used. For example, a quartz substrate,a silicon substrate, a non-alkaline glass substrate containing bariumborosilicate glass or aluminoborosilicate glass or the like, or asubstrate having an insulating film formed on a surface of a metalsubstrate can be used. Also a plastic substrate that is heat-resistantenough to be durable to the processing temperature may be used.

Next, an insulating film 11 is formed on the substrate 10. Theinsulating film 11 contains an insulating film such as a silicon oxidefilm, a silicon nitride film, a silicon oxynitride film or the like. Asshown in FIG. 1B, the insulating film 11 is formed to have a regularprojection and depression pattern. In other words, the insulating film11 is formed so that a depression and a projection are repeatedregularly.

Then, a semiconductor film 12 is formed on the insulating film 11. Thesemiconductor film 12 is formed on the insulating film 11 having theprojection and depression shape. As a result, also the semiconductorfilm 12 has a depression and projection shape as shown in FIG. 1C.

In the state as described above, a laser beam is irradiated on thesemiconductor film 12. Then, the semiconductor film 12 forms crystalshaving a plane orientation as shown in FIG. 1C. More specifically, asgrooves perpendicular to the surface of the substrate 10 are formed, Sicontact the side surfaces and bottom surfaces or top surfaces of thegrooves and therefore the (100) plane and (010) and (001) planesequivalent thereto, of Si contacting the respective surfaces, arerearranged to be in contact with each other. Therefore, single crystalshaving the same perpendicular direction to the substrate and the samein-plane direction parallel to the substrate are grown.

The method for manufacturing a semiconductor device of this embodimentmode may be combined with the method for manufacturing a semiconductordevice described in Embodiment Mode 1 with reference to FIGS. 3 to 5. Inthis case, the depression and projection shaped insulating film 11 isformed on the substrate 10, and a semiconductor film is formed on theinsulating film 11 and patterned into a desired shape, thus forming theisland-like semiconductor layer 12, as shown in FIG. 2A. Irradiating ofa laser beam spot is started at a pointed end part (top end) of theisland-like semiconductor layer 12. Since crystallization starts at thepointed end part (top end) of the island-like semiconductor layer 12, anisland-like semiconductor layer having a better property can beprovided.

The shape of the insulating film 11 is not limited to the depression andprojection shape as shown in FIG. 2A. For example, it may be atriangular shape as shown in FIG. 2B.

Steps in the method for manufacturing a semiconductor device using theprinciple of grapho-epitaxy are briefly shown in FIGS. 23 and 24.

In FIG. 23A, an base film 32 is first formed on a substrate 31. As thesubstrate 31, any material that is durable to the processing temperaturethroughout the manufacture of a semiconductor device may be used. Forexample, a quartz substrate, a silicon substrate, a non-alkaline glasssubstrate containing barium borosilicate glass or aluminoborosilicateglass or the like, or a substrate having an insulating film formed on asurface of a metal substrate can be used. Also a plastic substrate thatis heat-resistant enough to be durable to the processing temperature maybe used.

The base film 32 is formed on the substrate 31. The base film 32contains an insulating film such as a silicon oxide film, a siliconnitride film, a silicon oxynitride film or the like. In this case, thebase film 32 is formed to have a regular projection and depressionpattern as shown in FIG. 23A.

Then, a semiconductor film 33 is formed on the base film 32. Thesemiconductor film 33 is formed on the base film 32 having theprojection and depression shape. As a result, also the semiconductorfilm 33 has a projection and depression surface as shown in FIG. 23B.

Then, a laser beam 35 is irradiated on the semiconductor film 33. Acrystallized semiconductor film 34 is thus formed (FIG. 23C).

Next, the semiconductor film 34 is patterned into a desired shape, thusforming island-like semiconductor layers 36 (FIG. 24A). Gate wirings 37,source and drain wirings 38 and an interlayer insulating film 39 areformed on the island-like semiconductor layers 36 (FIG. 24B).

This embodiment mode can be optionally combined with Embodiment Mode 1.

Embodiment Mode 3

In this embodiment mode, top views in the case where a gate electrodeand source and drain wirings are formed on an island-like semiconductorlayer formed by using the methods for preparing a semiconductor devicedescribed in Embodiment Modes 1 and 2 will be described with referenceto FIGS. 6 to 9.

In FIG. 6, 1 represents a first island-like semiconductor layer, and 2and 4 represent a source wiring and a drain wiring, respectively or viceversa. 3 represents a gate electrode and 5 represents a contact hole.FIGS. 6A to 6C represent second island-like semiconductor layers.

In FIG. 4A, three second island-like semiconductor layers 105 are formedfrom a first island-like semiconductor layer 104. In this specification,the three first island-like semiconductor layers, from the side close toa-point, are referred to as second island-like semiconductor layer 6A,second island-like semiconductor layer 6B, and second island-likesemiconductor layer 6C. In the present invention, the second island-likesemiconductor layer 6A, the second island-like semiconductor layer 6Band the second island-like semiconductor layer 6C in three firstisland-like semiconductor layers 1 form a circuit, as shown in FIG. 6.

In the present invention, plural second island-like semiconductorsconstituting a unit circuit are formed from different first island-likesemiconductors. On the assumption that three second island-likesemiconductors form a unit circuit, the three second island-likesemiconductors are set to be at different distances from the pointed endpart (a-point). The different properties of the second island-likesemiconductors can be thus averaged. As a result, the properties of unitcircuits can be equalized.

Further, FIG. 7 shows the case where a multi-channel TFT is formed usingthree second island-like semiconductor layers. A second island-likesemiconductor layer 6D has a structure such that the second island-likesemiconductor layers 6A to 6C shown in FIG. 4 are combined. It ispreferred that the multi-channel TFT as shown in FIG. 7 is used for thecurrent mirror circuit shown in FIG. 10A.

Next, FIG. 8 shows the case where a TFT is formed using one secondisland-like semiconductor layer and plural first island-likesemiconductor layers 1 are separated.

Finally, FIG. 9 shows a circuit diagram of the semiconductor devicesshown in FIGS. 6 to 8.

This embodiment mode can be optionally combined with Embodiment Modes 1and 2.

EMBODIMENTS

Embodiments of the present invention will now be described.

Embodiment 1

This embodiment describes an example of a laser crystallization processusing a CW laser.

A CW laser suitable for the process is one having a wavelength of 550 nmor less and having highly stable output power. For example, the secondharmonic of a YVO₄ laser, the second harmonic of a YAG laser, the secondharmonic of a YLF laser, the second harmonic of a YAlO₃ laser, and an Arlaser and the like meet the requirement. Or higher harmonic of theselasers may also be used. Alternatively, a ruby laser, an alexandritelaser, a Ti:sapphire laser, a continuous wave excimer laser, Kr laser,CO₂ laser, a continuous wave helium cadmium laser, copper steam laser,gold steam laser or the like may be employed. It is also possible toemploy plural lasers of different types chosen from those lasers.

FIG. 12A is a schematic representation of an apparatus for CW lasercrystallization. The apparatus includes a laser oscillator 701, a mirror702, a convex lens 703, an X-Y stage 704, etc. The laser used here is anoutput 10 W power continuous wave YVO₄ laser. The laser oscillator 701is provided with a non-linear optical element and emits the secondharmonic from its exit.

A laser beam emitted from the laser oscillator 701 has a circular shapeas indicated by A in FIG. 12A. The laser beam is emitted in thehorizontal direction and is deflected by the mirror 702 toward thedirection about 20° from the vertical direction. Thereafter, the beam iscollected by the convex lens 703 positioned in the horizontal direction.A substrate 705 is fixed to the X-Y stage 704 and an irradiation surfaceon a semiconductor layer that is formed on the substrate is brought tothe focus of the convex lens 703. At this point, the irradiation surfaceis arranged such that it is in parallel with the convex lens 703. Inother words, the substrate 705 is arranged horizontally. The laser beamenters the convex lens 703 at about 20° and therefore the laser beamforms an elliptical shape on the irradiation surface due to astigmatismof the convex lens. The laser beam shape on the irradiation surface isdetermined by the incident angle at which the laser beam enters theconvex lens 703. Accordingly, the laser beam can have an ellipticalshape of larger aspect ratio by making it enter the convex lens at alarger angle to the vertical direction. On the other hand, this makesthe focal depth shallow and uniform irradiation difficult. The suitabledeflection angle is therefore about 20°.

In order to crystallize semiconductor layers on the entire surface ofthe substrate, it is necessary to repeatedly run an elliptical beam overthe substrate at a suitable irradiation pitch while shifting the beam inits longer diameter direction. This operation is achieved by fixing alaser output unit that includes the laser oscillator 701, the mirror702, and the convex lens 703 using the X-Y stage 704 to move thesubstrate in a manner that makes the elliptical beam run over thesubstrate. When the substrate, i.e., the irradiation object, measures600 mm in the X direction and 720 mm in the Y direction and theelliptical beam measures 200 μm in the longer diameter direction, itrequires 3000 times of laser scanning (1500 times of reciprocation) inthe direction shown in FIG. 12A to irradiate the entire surface of thesubstrate.

As described in detail in following embodiments, the number of scanningcan be reduced and the processing time can be shortened by using plurallaser oscillators and scanning the substrate with plural ellipticalbeams arranged side by side in the longer diameter direction of theellipse. Thus, low energy density portions at both the edges of a singlelaser beam overlap each other at the edges of adjacent laser beams,thereby raising the energy density. As a result, the effectiveirradiation region is widened and the ratio of the effective irradiationregion to the whole irradiation region in one irradiation is increasedto further reduce limitations in circuit layout.

This embodiment can be implemented by freely combining with EmbodimentModes 1 to 3.

Embodiment 2

This embodiment gives a description with reference to FIG. 12B on anexample of using an optical system different from the one in Embodiment1 to polarize a laser beam.

A laser beam emitted from a laser oscillator 801 has a circular shape asindicated by A in FIG. 12B. The laser beam is emitted in the horizontaldirection and is reflected by a mirror 802 toward the verticaldirection. Thereafter, the beam is collected by a first cylindrical lens803 in the X direction. At this point, the circular shape of the laserbeam is collected in the X direction and an elliptical shape with thelonger diameter set in the Y direction is formed as indicated by B inFIG. 12B. The laser beam is then collected by a second cylindrical lens804 in the Y direction. At this point, the laser beam is furthercollected in the Y direction and an elliptical shape with the longerdiameter set in the X direction is formed as indicated by C in FIG. 12B.This optical system can provide an elliptical beam having an aspectratio even larger than that of the laser beam shown in Embodiment 2.Then, a substrate 806 fixed to an X-Y stage 805 is irradiated Laser beamscanning over the substrate may be performed in the way shown inEmbodiment 3.

The number of scanning can be reduced and the processing time can beshortened by using plural laser oscillators and scanning the substratewith plural elliptical beams arranged in parallel side by side in thelonger diameter direction of the ellipse. Thus, low energy densityportions at both the edges of a single laser beam overlap each other atthe edges of adjacent laser beams, thereby raising the energy density.As a result, the effective irradiation region is widened and limitationsin circuit layout can be further reduced.

This embodiment can be implemented by freely combining Embodiment Modes1 to 3 and Embodiment 1.

Embodiment 3

When crystallizing the semiconductor layer by using the CW laseraccording to the steps described in the embodiment modes, the shape oflaser light oscillated by a single laser oscillator on a surface to beirradiated is either elliptical or rectangular. The laser light isconverged into a spot state to increase the energy density on theirradiation surface, and the irradiation range is therefore as shown inFIG. 13A.

The energy density is further distributed in the laser light convergedinto the spot state. FIG. 13B shows an energy distribution in thelongitudinal direction and on an X cross-sectional plane, that is, inthe longitudinal-axis direction of the ellipse in FIG. 13A.

As is shown in FIG. 13B, in the laser-light spot, a distribution isexhibited such that the energy density gradually decreases in thedirection from the central portion to the end portion. In the drawing,the symbol “E” denotes an energy density minimally required forsatisfactory crystallization of the semiconductor layer. FIG. 13C showsa state where the semiconductor layer irradiated with laser light in arange D is crystallized satisfactorily, thereby proving that thesemiconductor has high electrical characteristics. However, in a regionof the semiconductor layer irradiated with laser light in a range d,since the energy density of the laser light is insufficient, meltingability is insufficient, thereby causing micro crystallization. In thisregion, since sufficient electrical characteristics cannot be obtained,the region is not suitable for use as an active layer.

For manufacturing a plurality of TFTs using the semiconductor layerobtained by patterning the single first island-like semiconductor layeras in the present invention, the range is desirably wider than that ofthe region D. However, since the increasing of the laser-light spot sizeis limited, when a circuit is configured within the limited width,difficulties arise in determining the layout of elements. Consequently,wirings and the like need to be led out long, thereby making aninefficient circuit layout.

In this embodiment, an example for implementing efficient laserirradiation by using laser light that is output from a plurality oflaser oscillators will be described.

Referring to FIG. 13D, reference numerals 401 to 403 denote spots oflaser light that have individually been output from three differentlaser oscillators and that have been converged into spot states throughoptical systems. The individual laser-light spots 401 to 403 aresynthesized into one laser-light spot, by aligning the longitudinal axesof the individual ellipses linear and partly overlapping with oneanother.

With reference numerals 404 to 406, FIG. 13E shows energy densitydistributions of the individual laser-light spots 401 to 403 in thelongitudinal-axis direction. The energy densities of the individualspots are identical, in which values of the peaks are denoted by “E₀”.With regard to the synthesized laser light spot, the energy densities ofthe overlapped regions are added together, thereby exhibiting energydensity distributions as shown with numeral 407 in FIG. 13E.

In this case, the energy densities of the two spots are added togetherin each of the regions where the adjacent spots 404 and 405 areoverlapped and where the adjacent spots 405 and 406 are overlapped. Eachof the regions has an energy density that is sufficient for satisfactorycrystallization of the semiconductor layer. Therefore, after thesynthesization, the shape of the spot is changed into a shape as shownwith numeral 408 in FIG. 13F. In this case, a range in whichsatisfactory crystallization of the semiconductor layer can be performedis as denoted by “D₀”.

The sum of energy densities of the regions where the adjacent spots areoverlapped is ideally identical to the peak value E₀ of the single spot.However, the spot-overlapping width may appropriately be set within therange D₀ to a value range suitable for obtaining satisfactory anduniform crystallization of the semiconductor layer.

Thus, as can be seen from FIG. 13D and FIG. 13F, the laser irradiationcan be implemented with the increased width in the manner that theplurality of laser-light spots are overlapped, and regions of low energydensities are mutually compensated.

Incidentally, use of the synthesized laser light spot is advantageousnot only in that a wide area can be scanned, but also in the efficiency.While the width of the irradiated region is (D+2d) when a single laserlight spot is used, the width of the irradiated region is (D₀+2d) when asynthesized laser light spot as shown in FIG. 13F is used. In the formercase, the ratio of the width in which satisfactory crystallization canbe performed to one-scanning width of the laser light spot is(D/(D+2d)), whereas the aforementioned ratio is (D₀/D₀+2d) in the lattercase. Due to D<D₀, it can be the that satisfactory crystallization canbe implemented more efficiently.

In addition, when using the synthesized laser light spot, as shown inFIG. 13G, the region where the energy density is low, situated at bothends in the longitudinal-axis direction is desirably shielded using aslit 409 not to be incident on the semiconductor layer. At this time,the spot on the surface of the semiconductor layer is shaped as shown inFIG. 13H, the spot is shaped similar to a rectangular having a width ofD₁(<D₀) in the longitudinal-axis direction.

When using the laser light spot shaped as described above to irradiatethe semiconductor layer, a region where the energy density is low doesnot exist in the light spot. Even if such a region exists, the widththereof is very small in comparison to a case without the slit beingused and thus facilitates control of the spot position to be performedfor preventing irradiation end portions of the laser light spot frombeing scanned over the first island-like semiconductor layer.Accordingly, the above arrangement enables reductions of constraints ondeterminations of the laser-light scanning path and the layout of eitherthe first island-like semiconductor layers or the second island-likesemiconductor layers.

Furthermore, by using the slit, the width of the laser light spot can bechanged with the energy density being maintained constant and withoutterminating the output of the laser oscillator. Hence, irradiation endportions of the laser light spot can be prevented from being scannedover the second island-like semiconductor layer or the channel formationregion thereof. Furthermore, the laser light can be irradiated also ontounnecessary regions of the substrate, thereby enabling effects to beexpected for preventing the substrate from being damaged.

The present embodiment can be implemented by freely combining withEmbodiment Modes 1 to 3 and Embodiments 1 and 2.

Embodiment 4

Hereinbelow, the configuration including a control system of a laserirradiation device used in the present invention will be described withreference to FIG. 14A. Reference numeral 901 denotes each of a pluralityof laser oscillators. While the configuration of FIG. 14A uses threelaser oscillators, the number of laser oscillators used for the laserirradiation device is not limited thereto.

The laser irradiation device of FIG. 14A includes a computer 908 thatincludes a central processing unit and storage means such as a memory.The computer 908 is capable of controlling the oscillation of laseroscillators 901 and moving a substrate to a predetermined position suchthat the position of the irradiation of a laser light spot onto thesubstrate 906 is controlled to cause the laser light spot to cover aregion determined according to mask-pattern information.

The laser oscillator 901 may maintain the temperature thereof to beconstant by using a chiller 902. The chiller 902 need not necessarily beprovided. However, by maintaining the temperature of the laseroscillator 901 to be constant, the energy of laser light to be outputcan be prevented from being varied by the temperature.

Reference numeral 904 denotes an optical system 904 that is capable ofconverging the laser light in such a manner as to change the path oflight that has been output from the laser oscillator 901 and to arrangea shape of the laser light spot. In addition, in the laser irradiationdevice of FIG. 14A, laser light spots that have been output from theplurality of laser oscillators 901 are partly overlapped with each otherthrough the optical system 904, and can thus be synthesized.

A plurality of AO modulators 903 capable of temporarily and completelyblocking the laser light may be provided in light paths between thesubstrate to be processed and the laser oscillators 901. Alternatively,instead of the AO modulators 903, attenuators may be provided to adjustthe energy density of the laser light.

The configuration may be modified such that means 910 for measuring theenergy density of the laser light that has been output from the laseroscillator 901 is provided in the light path between the substrate 906which is an object to be processed and the laser oscillator 901, andvariations with time in the measured energy density are monitored usingthe computer 908. In this case, the output of the laser oscillator 901may be increased to compensate for attenuation in the energy density ofthe laser light.

The synthesized laser light spot is irradiated onto the substrate 906which is an object to be processed via the slit 905. Desirably, the slit905 is capable of blocking the laser light, and is formed of a materialhaving sufficient resistance against damage or deformation that can becaused by laser light. In addition, the slit width of the slit 905 isvariable so that the width of the laser light spot can be changedaccording to the slit width.

When laser light oscillated by the laser oscillator 901 is not passedthrough the slit 905, the shape of the laser light spot on the substrate906 is variable depending on the laser type, and can be rectifiedthrough the optical system.

The substrate 906 is mounted on an X-Y stage 907. In FIG. 14A, the X-Ystage 907 is controlled by a computer, and the irradiation position ofthe laser light spot is controlled by moving the object to be processed,that is, the substrate 906.

In the present invention, according to the computer 908, the width ofthe slit 905 is controlled, and the width of the laser light spot can bechanged according to pattern information of a mask.

In addition, the laser irradiation device shown in FIG. 14A may includemeans for adjusting the temperature of the object to be processed.Further, since the laser light has high directivity and energy density,a damper may be provided to prevent reflected light from beingirradiated onto an inappropriate portion. Desirably, the damper has aproperty of adsorbing reflected light, and cooling water is circulatedin the damper to prevent the temperature of partition walls from beingrisen due to the absorption of reflected light. In addition, means(substrate-heating means) for heating the substrate 906 may be providedto the X-Y stage 907.

In a case where the alignment marker is to be formed using the laser, amarker-dedicated laser oscillator may be provided. In this case,oscillation of the marker-dedicated laser oscillator may be controlledusing the computer 908. In the case where the marker-dedicated laseroscillator is provided, a separate optical system should be provided toconverge laser light emitted from the marker-dedicated laser oscillator.A YAG laser and a CO₂ laser are representative lasers that are used forthe formation of the marker. Of course, a different laser can be used toform the marker.

One CCD camera 909 may be provided to perform alignment by using themarker. Depending on the necessity, two or more CCD cameras 909 may beprovided.

Even when no specific marker is provided, the alignment can be performedby recognizing the pattern of the first island-like semiconductor layerby means of the CCD camera 909. Mask-attributed pattern information ofthe first island-like semiconductor layer that has been input to thecomputer 908 is compared with the actual pattern information of thefirst island-like semiconductor layer that has been stored in the CCDcamera 909. As a result, information regarding the position of thesubstrate can be obtained. In this case, no specific marker needs to beprovided.

With reference to FIG. 14A, the configuration including the plurality oflaser oscillators has been described, but the configuration may bemodified to include one laser oscillator. FIG. 14B shows theconfiguration of a laser irradiation device using one laser oscillator.Referring to FIG. 14B, numeral 901 denotes a laser oscillator, andnumeral 902 denotes a chiller. Numeral 910 denotes an energy densitymeasuring device, numeral 903 denotes an AO modulator, numeral 904denotes an optical system, a numeral 905 denotes a slit, and numeral 909denotes a CCD camera. A substrate 906 is mounted on an X-Y stage 907,whereby the position of irradiation of a laser light spot onto asubstrate 906 is controlled. Similar to the configuration shown in FIG.14A, operations of the individual means included in the laserirradiation device are controlled by the computer 908. Dissimilar to theconfiguration of FIG. 14A, however, the present configuration includesthe one laser oscillator. Accordingly, unlike the configuration of FIG.14A, also the optical system 904 may be provided with a function toconverge laser light emitted from one laser source.

FIG. 15A shows an example of the relationship between the shape of maskfor patterning a semiconductor layer and the width of a laser light spot2001 when laser light is irradiated one time. Numeral 2002 denotes aportion scanned with a beam spot having a width W₃ obtained bysynthesizing overlapped beams of laser light that have been output fromfour laser oscillators. Numeral 2001 denotes a portion scanned with abeam spot having a width W₄ obtained by synthesizing overlapped beams oflaser light that have been output from three laser oscillators. Thescanning width may be controlled through the slit; or output of aportion of the laser light may be stopped, or may be blocked using theAO modulator.

As in this embodiment, when the AO modulator is used, the width of thelaser light spot 2001 can arbitrarily be changed without terminatingoutput operations of all the laser oscillators. This enables the outputto be prevented from being unstable due to termination of the outputoperation of the laser oscillator.

According to the configuration described above, since the width of thetrail of the laser light can be changed, even when the width of thefirst island-like semiconductor layer is partly different as shown inFIG. 15A, edges of the trail of the laser light can be prevented fromoverlapping a semiconductor that is obtained by a patterning process. Inaddition, this embodiment enables the reduction in the probability ofcausing damage occurring on the substrate because of irradiation of thelaser light onto unnecessary portions.

Hereinbelow, a description will be made regarding an example in whichlaser light is blocked by the AO modulator during laser-lightirradiation so that the laser light is irradiated only onto apredetermined portion. While the laser light is thus blocked, thepresent invention is not limited thus, and any other means capable ofblocking the laser light may be used.

In the present invention, portions scanned with the laser light aregrasped by the computer according to the mask information that has beeninput. In addition, in this embodiment, the AO modulator is used toblock the laser light to be irradiated only onto a (predetermined)portion required to be scanned. In this case, the AO modulator isdesirably capable of blocking the laser light and is formed of amaterial having sufficient resistance against deformation or damage thatcan be caused by the laser light.

FIG. 15B shows an example of the relationship between the shape of amask for patterning a semiconductor layer and portions irradiated withthe laser light. Reference numeral 2001 denotes a laser light spot, andreference numeral 2004 denotes portions irradiated with the laser light.As shown in FIG. 15B, when scanning the portion where the firstisland-like semiconductor layer is not formed, the laser light isblocked by the AO modulator, and the laser light is therefore notirradiated onto the substrate. According to this embodiment, the laserlight can be controlled not to be irradiated onto a portion that neednot be crystallized; and even when the laser light has been irradiatedthereonto, the energy density of the laser light can be controlled low.Therefore, this embodiment enables further reduction in the probabilityof causing damage occurring on the substrate due to irradiation of thelaser light onto unnecessary portions.

The present embodiment can be implemented by freely combining withEmbodiment Modes 1 to 3 and Embodiments 1 to 3.

Embodiment 5

In this embodiment, a process flow of steps in a semiconductor-devicemanufacturing method of the present invention will be described.

FIG. 16A shows a process flow of manufacturing steps. First, a CAD(computer aided design) system is used to design a circuit of asemiconductor device. When a circuit layout has been determined, thatis, when TFT layout has been determined, the forming position of theeach second island-like semiconductor layer is concurrently determined.In this case, the second island-like semiconductor layer, which isincluded in one first island-like semiconductor layer, is desirablydetermined to be positioned such that the charge movement direction inthe channel forming region is either aligned parallel to the scanningdirection of the laser light or is aligned along an equivalentdirection. However, the direction may not intentionally be aligneddepending on the usage.

In addition, in the above step, a mask of the first island-likesemiconductor layer may be designed so that a marker is formed togetherwith the first island-like semiconductor layer.

Subsequently, information regarding the pattern of the mask (patterninformation) of the designed first island-like semiconductor layer isentered into the computer included in the laser irradiation device.According to the entered pattern information of the first island-likesemiconductor layers, the computer calculates the width of the eachfirst island-like semiconductor layer in the vertical direction to thescanning direction. Then, the width of the slit in the verticaldirection to the scanning direction is set according to the width of theeach first island-like semiconductor layer.

Subsequently, according to the slit width, a scanning path of the laserlight is determined based on the marker position as a reference.

On the other hand, films are deposited on the semiconductor substrate,the mask of the first island-like semiconductor layers is used topattern the semiconductor layer, and the first island-like semiconductorlayers are then formed. Subsequently, the substrate on which the firstisland-like semiconductor layers are formed is set over the stage of thelaser irradiation device.

Subsequently, using the marker as a reference, the laser light isirradiated along the determined scanning path, and crystallization isperformed targeting the first island-like semiconductor layer.

After the laser light has been irradiated, patterning is performed forthe first island-like semiconductor layer enhanced in the crystallinityaccording to the laser-light irradiation, and second island-likesemiconductor layers are then formed. Thereafter, steps of manufacturinga TFT from the second island-like semiconductor layer are performed.Specifically, TFT-manufacturing steps are variable depending on theshape of the TFT. Representatively, however, a gate insulating film isdeposited, and an impurity region is formed in the second island-likesemiconductor layer. Subsequently, an interlayer insulating film isformed in such a manner as to cover the gate insulating film and a gateelectrode, and contact holes are formed through the interlayerinsulating film, and the impurity region is partly exposed. Then,wirings are formed on the interlayer insulating film to be in contactwith the impurity region through the contact holes.

Next, a description will be given regarding an example procedure ofperforming alignment of the substrate and the mask by using the CCDcamera, without forming an alignment marker.

FIG. 16B shows a process flow of manufacturing steps. First, similar tothe case of FIG. 16A, a CAD system is used to design a circuit of asemiconductor device. When a circuit layout has been determined, thatis, when TFT layout has been determined, the forming position of theeach second island-like semiconductor layer is concurrently determined.In this case, the second island-like semiconductor layer, which isincluded in one first island-like semiconductor layer, is desirablydetermined to be positioned such that the charge movement direction inthe channel forming region is either aligned parallel to the scanningdirection of the laser light or is aligned along an equivalentdirection. However, the direction may not intentionally be aligneddepending on the usage.

Subsequently, information regarding the pattern of the mask (patterninformation) of the designed first island-like semiconductor layer isentered into the computer included in the laser irradiation device.According to the entered pattern information of the first island-likesemiconductor layers, the computer calculates the width of the eachfirst island-like semiconductor layer in the vertical direction to thescanning direction. Then, the width of the slit in the verticaldirection to the scanning direction is set according to the width of theeach first island-like semiconductor layer.

On the other hand, the semiconductor layers are deposited on thesubstrate, the mask of the first island-like semiconductor layers isused to pattern the semiconductor layer, and the first island-likesemiconductor layers are then formed. Subsequently, the substrate onwhich the first island-like semiconductor layers are formed is set overthe stage of the laser irradiation device.

Subsequently, pattern information of the first island-like semiconductorlayers formed on the substrate set over the stage is detected by the CCDcamera, and is then input as information to the computer. The computercompares two pieces of information. One of the two pieces of informationis the pattern information of the first island-like semiconductor layerdesigned by the CAD system; and the other is the CCD-camera-obtainedpattern information of the first island-like semiconductor layeractually formed on the substrate. As a result, the substrate and themask are aligned with each other.

Subsequently, a scanning path of the laser light is determined accordingto the slit width and the CCD-camera-obtained position information ofthe first island-like semiconductor layer.

Then, the laser light is irradiated along the determined scanning path,and crystallization is performed targeting the first island-likesemiconductor layer.

After the laser light has been irradiated, patterning is performed forthe first island-like semiconductor layer enhanced in the crystallinity,and second island-like semiconductor layers are then formed. Thereafter,the steps of manufacturing a TFT from the second island-likesemiconductor layer are performed. Specifically, TFT-manufacturingprocedure is variable depending on the shape of the TFT.Representatively, however, a gate insulating film is deposited, and animpurity region is formed in the second island-like semiconductor layer.Subsequently, an interlayer insulating film is formed in such a manneras to cover the gate insulating film and a gate electrode, and contactholes are formed through the interlayer insulating film, and theimpurity region is partly exposed. Then, wirings are formed on theinterlayer insulating film to be in contact with the impurity regionthrough the contact holes.

Next, an example method according to which laser-light irradiation isperformed multiple times will be described. As an example, a descriptionwill be made with reference to a method of performing second-time laserirradiation by changing the direction after laser irradiation has beenperformed one time.

FIG. 17A shows a process flow of manufacturing steps. First, a CADsystem is used to design a circuit of a semiconductor device. When acircuit layout has been determined, that is, when TFT layout has beendetermined, the forming position of each second island-likesemiconductor layer is concurrently determined. In this case, the secondisland-like semiconductor layer, which is included in one firstisland-like semiconductor layer, is desirably determined to bepositioned such that the charge movement direction in the channelforming region is either aligned parallel to the scanning direction ofthe laser light or is aligned along an equivalent direction. However,the direction may not intentionally be aligned depending on the usage.

Subsequently, information regarding the pattern of the mask (patterninformation) of the designed first island-like semiconductor layer isentered into the computer included in the laser irradiation device.According to the entered pattern information of the first island-likesemiconductor layers, the computer calculates two widths of the eachfirst island-like semiconductor layer in the vertical direction to eachof the two scanning directions. Then, the widths of the slit in thevertical direction to each of the two scanning directions are calculatedaccording to the widths of the each first island-like semiconductorlayer.

Subsequently, based on each of the determined slit widths, scanningpaths of the laser light are determined in the individual two scanningdirections according to the marker position as a reference.

On the other hand, the semiconductor layers are formed on the substrate,the mask of the first island-like semiconductor layers is used topattern the semiconductor layer, and the first island-like semiconductorlayers are then formed. Subsequently, the substrate on which the firstisland-like semiconductor layers are formed is set over the stage of thelaser irradiation device.

Subsequently, using the marker as a reference, first laser light isirradiated along the first one of the two scanning paths that have beendetermined, and crystallization is performed targeting the firstisland-like semiconductor layer.

Subsequently, after changing the scanning direction, second laser lightis irradiated along the second scanning path, and crystallization isperformed targeting the first island-like semiconductor layer.

The angles of the scanning directions of the first laser light andsecond laser light may either be pre-stored in a memory or the like ormanually be entered each time.

FIG. 17A shows an example method according to which the laser light isirradiated two times to the same first island-like semiconductor layer.However, with an AO modulator or the like being used, the scanningdirection can be changed by specifying positions. For example, a case isassumed such that the scanning direction in a signal-line drive circuitis set different from the scanning direction in a pixel portion and ascan-line drive circuit. In this case, when an AO modulator is used toirradiate laser light to a position where the signal-line drive circuitis formed, the laser light can be controlled using the AO modulator notto be irradiated onto positions where the pixel portion and scan-linedrive circuit are formed. When an AO modulator is used to irradiatelaser light onto a position where the pixel portion and a scan-linedrive circuit are formed, the laser light can be controlled using the AOmodulator not to be irradiated onto a position where the signal-linedrive circuit is formed. In this case, the AO modulator is controlled bythe computer to operate in synchronization with position control means.

After the laser light has been irradiated, patterning is performed forthe first island-like semiconductor layer enhanced in the crystallinity,and second island-like semiconductor layers are then formed. Thereafter,steps of manufacturing a TFT from the second island-like semiconductorlayer are performed. Specifically, TFT-manufacturing steps are variabledepending on the shape of the TFT. Representatively, however, a gateinsulating film is deposited, and an impurity region is formed in thesecond island-like semiconductor layer. Subsequently, an interlayerinsulating film is formed in such a manner as to cover the gateinsulating film and a gate electrode, and contact holes are formedthrough the interlayer insulating film, and the impurity region ispartly exposed. Then, wirings are formed on the interlayer insulatingfilm to be in contact with the impurity region through the contactholes.

For comparison, FIG. 17B shows a process flow of manufacturing steps fora conventional semiconductor layers. As shown in FIG. 17B, a CAD systemis used to design a mask of a semiconductor device. On the other hand,an amorphous semiconductor layer is deposited on the substrate, and asubstrate on which the amorphous semiconductor layer is formed is setover the laser irradiation device. Subsequently, scanning is performedso that laser light is irradiated onto the entire surface of theamorphous semiconductor layer, and the amorphous semiconductor layer isthus crystallized. Then, an alignment marker is formed on apolycrystalline semiconductor layer thus obtained throughcrystallization, and the polycrystalline semiconductor layer ispatterned using the alignment marker as a reference. In this manner,second island-like semiconductor layers are formed. Subsequently, TFTsare formed using the second island-like semiconductor layers.

As described above, dissimilar to the conventional case shown in FIG.17B, according to the present invention, the alignment marker is formedusing the laser light before the amorphous semiconductor layer iscrystallized. Thereafter, the laser light is scanned according to theinformation of the mask for patterning the semiconductor layers.

According to the configuration described above, there can be reduced atime for irradiating the laser light to portions that are to be excludedby pattering among the semiconductor layers on the substrate.Consequently, the time for laser-light irradiation can be reduced, andin addition, the substrate-processing speed can be improved.

The method may include a step of crystallizing the semiconductor film byusing a catalyst prior to the step of crystallization using the laserlight. When using a catalytic element, a technique disclosed in eitherJP 07-130652 A and/or JP 08-78329 A is desirably employed.

The method including the step of crystallizing the semiconductor layerby using a catalyst includes a step of performing Ni-usingcrystallization (NiSPC) after deposition of an amorphous semiconductorlayer. For example, when employing the technique disclosed in JP07-130652 A, a nickel-containing layer is formed by coating an amorphoussemiconductor layer with a nickel acetate solution containing nickel 10ppm by weight. The nickel-containing layer is subjected to a step ofdehydrogenation at 500° C. for one hour, and is then subjected to heattreatment at 500 to 650° C. for 4 to 12 hours, for example, at 550° C.for 8 hours. In this case, in addition to nickel (Ni), usable catalyticelements such as germanium (Ge), ferrous (Fe), palladium (Pd), tin (Sn),lead (Pb), cobalt (Co), platinum (Pt), copper (Cu), and gold (Au) may beused.

The crystallinity of the semiconductor layer crystallized according tothe NiSPC is further enhanced through laser-light irradiation. Since apolycrystalline semiconductor layer obtained through the laser-lightirradiation contains the catalytic element, the layer is subjected to astep (gettering step) of removing the catalytic element from theamorphous semiconductor layer after the laser irradiation. The getteringstep may be performed using a technique disclosed in JP 10-135468 A orJP 10-135469 A.

Specifically, phosphorous is partly added to the polycrystallinesemiconductor layer obtained after the laser-light irradiation, and heattreatment is performed at 550 to 800° C. for 5 to 24 hours, for example,at 600° C. for 12 hours, in a nitrogen atmosphere. As a result, aphosphorous-added region of the polycrystalline semiconductor layerworks as a gettering site, thereby enabling phosphorous existing in thepolycrystalline semiconductor layer to segregate to the gettering site.Thereafter, the phosphorous-added region of the polycrystallinesemiconductor layer is removed by patterning. Consequently, theprocesses as described above enables the production of a secondisland-like semiconductor layers that have a catalytic-elementconcentration reduced below 1×10¹⁷ atms/cm³, preferably to a level of1×10¹⁶ atms/cm³.

The present embodiment can be implemented by freely combining withEmbodiment Modes 1 to 3 and Embodiments 1 to 4.

Embodiment 6

In this embodiment, circuit layouts on substrates, CW laser irradiationdirections, and the like will be described with reference to someexamples.

Generally, a display device is configured as an example shown in FIG.18A. The general example display device is configured to include a pixelportion 1401 in a central portion of a substrate 1400, asource-signal-line drive circuit 1402 in an upper or lower portion ofthe pixel portion 1401, and a gate-signal-line drive circuit 1403 in anyone of left and right portions of the pixel portion 1401 or in both ofthe left and right portions of the pixel portion 1401. A signal andpower for driving the each drive circuit is input via a flexible printedcircuit (FPC) 1404 from the outside of the substrate.

As shown in FIG. 18A, the source-signal-line drive circuit 1402 isdisposed extending in a pixel-column direction, and the gate-signal-linedrive circuit 1403 is disposed extending in a pixel-line direction.Therefore, in a case where CW laser irradiation is performed asdescribed in the Embodiment Modes, when the irradiation direction isaligned along the disposition direction of the source-signal-line drivecircuit, as shown in FIG. 18B, the irradiation direction of the CW laseris not aligned to the disposition direction of the gate-signal-linedrive circuit. Generally, however, in comparison to a source-signal-linedrive circuit for which high-speed driving is required, the drivingfrequency of a gate-signal-line drive circuit may be about one-severalhundredth. Accordingly, even if active layers of TFTs constituting thegate-signal-line drive circuit are formed to include portions ofmicrocrystalline semiconductor layers, it can be said that no problemswould occur with the circuit operation.

FIG. 18C illustrates another usable method in which the scanningdirection is shifted on the way. Specifically, first laser scanning isfirst performed in alignment with the source-signal-line drive circuit.Then, a stage on which the substrate is fixed is rotated 90 degrees, thelaser scanning direction is thus changed, and second CW laserirradiation is then performed in alignment to the gate-signal-line drivecircuit and the pixel portion.

FIG. 18D illustrates still another usable method using a techniquedisclosed in Japanese Patent Application No. 2001-241463. In this case,a source-signal-line drive circuit 1402 and a gate-signal-line drivecircuit 1403 are either disposed on one side of a pixel portion or aredisposed parallel to each other on the opposing two sides of the pixelportion. As a result, as shown in FIG. 14E, crystallization can becompleted by one-time CW laser irradiation; and concurrently, the pixelportion and a semiconductor layer in a drive circuit can be configuredonly by unidirectional laser-light irradiation.

The above described method in this embodiment is only one example ofmany methods. For example, a method may be used in which only a drivecircuit portion for which high-speed driving is required is crystallizedby the laser-light irradiation, and a pixel portion and the like forwhich the requirement level for high-speed driving is relatively low aremanufactured using a conventional crystallization method. Meanwhile,this embodiment may be implemented in combination with otherembodiments.

The present embodiment can be implemented by freely combining withEmbodiment Modes 1 to 3 and Embodiments 1 to 5.

Embodiment 7

In this embodiment, a method of manufacturing an active matrix substratewill be described with reference to FIGS. 19 and 20. A substrate onwhich a drive circuit including a CMOS circuit and a pixel portion areformed together is referred to as active matrix substrate forconvenience.

First of all, a substrate 5001 formed of glass such as bariumborosilicate glass and aluminum borosilicate glass is used in thisembodiment. The substrate 5001 may be a quartz substrate, a siliconsubstrate, a metal substrate or stainless substrate which has aninsulating film on the surface. The substrate 5001 may be a plasticsubstrate having heat resistance, which withstands a processingtemperature in this embodiment.

Next, a base film 5002 having an insulating film such as silicon oxidefilm, silicon nitride film, and a silicon oxynitride film is formed onthe substrate 5001 by publicly known method (such as the sputtering,LPCVD and plasma CVD). In this embodiment, a two-layer structurecomposing base films 5002 a and 5002 b is used for the base film 5002.However, a structure may be used where a single layer film is used or atleast two layers are stacked.

Next, semiconductor layer 5003 is formed with a thickness of 25 to 80 nm(preferably 30 to 60 nm) by publicly known method (such as thesputtering, LPCVD and plasma CVD) on the base film 5002. Thesemiconductor layer may be an amorphous semiconductor layer, a microcrystal semiconductor layer or a crystalline semiconductor layer.Alternatively, the semiconductor layer may be a compound semiconductorlayer having an amorphous structure such as an amorphous silicongermanium film (FIG. 19A).

The semiconductor layer 5003 is patterned. And the first island-likesemiconductor layers 5004 to 5006 are formed by the anisotropic dryetching (the first etching treatment) in an atmosphere containinghalogen fluoride, for example, ClF, ClF₃, BrF, BrF₃, IF, IF₃, and thelike (FIG. 19B).

Then, the first island-like semiconductor layers 5004 to 5006 arecrystallized by laser crystallization method. In the case that thesemiconductor layer is a micro crystal semiconductor layer orcrystalline semiconductor layer, its crystallinity of the island-likesemiconductor layers is enhanced by conducting this step. The lasercrystallization method is conducted by using the laser irradiationmethod described in Embodiment Modes and Embodiments 1 to 6.Specifically, the first island-like semiconductor layers 5004 to 5006are selectively subjected to laser light according to the maskinformation inputted to a computer of the laser irradiation apparatus.Of course, in addition to the laser crystallization method, thesemiconductor layer may be crystallized by combining other publiclyknown crystallization method (such as thermal crystallization methodusing RTA or a furnace annealing kiln and thermal crystallization methodusing a metal element facilitating the crystallization).

When a crystallization of a semiconductor layer is conducted, it ispreferable that the second harmonic through the fourth harmonic of basicwaves is applied by using the solid state laser which is capable ofcontinuous oscillation in order to obtain a crystal in large grain size.Typically, it is preferable that the second harmonic (with a wavelengthof 532 nm) or the third harmonic (with a wavelength of 355 nm) of anNd:YVO₄ laser (basic wave of 1064 nm) is applied. Specifically, laserbeams emitted from the continuous oscillation type YVO₄ laser with 10 Woutput is converted into a harmonic by using the non-linear opticalelements. Also, a method of emitting a harmonic by applying crystal ofYVO₄ and the non-linear optical elements into a resonator may be used.Then, more preferably, the laser beams are formed on an irradiationsurface so as to have a rectangular shape or an elliptical shape throughan optical system, thereby irradiating a substance to be treated. Atthis time, the energy density of approximately 0.01 to 100 MW/cm²(preferably 0.1 to 10 MW/cm²) is required. The substrate 5001 on whichsemiconductor film is formed is moved at approximately 10 to 2000 cm/srate relatively corresponding to the laser beams so as to irradiate thesemiconductor film.

Note that, a gas laser or solid-state laser of continuous oscillationtype or pulse oscillation type can be used. The gas laser such as anexcimer laser, Ar laser, Kr laser and the solid-state laser such as YAGlaser, YVO₄ laser, YLF laser, YAlO₃ laser, glass laser, ruby laser,alexandrite laser, Ti:sapphire laser can be used as the laser beam.Also, crystals such as YAG laser, YVO₄ laser, YLF laser, YAlO₃ laserwherein Cr, Nd, Er, Ho, Ce, Co, Ti or Tm is doped can be used as thesolid-state laser. A basic wave of the lasers is different depending onthe materials of doping, therefore a laser beam having a basic wave ofapproximately 1 μm is obtained. A harmonic corresponding to the basicwave can be obtained by the using non-linear optical elements.

The first island-like semiconductor layers 5004 to 5006 are subjected tolaser light and enhanced the crystallinity by the above mentioned lasercrystallization (FIG. 19C).

The second island-like semiconductor layers 5008 to 5011 are formed byconducting patterning (the second etching treatment) of the enhancedcrystallized first island-like semiconductor layers 5004 to 5006 into adesired shape (FIG. 19D).

After the second island-like semiconductor layers 5008 to 5011 areformed, a small amount of impurity element (boron or phosphorus) may bedoped in order to control a threshold value of the TFT.

Next, a gate insulating film 5012 covering the second island-likesemiconductor layers 5008 to 5011 is formed. The gate insulating film5012 is formed by using an insulating film containing silicon with athickness of 40 to 150 nm by using plasma CVD or sputtering. In thisembodiment, a silicon oxynitride film (compositional ratio: Si=32%,O=59%, N=7% and H=2%) with a thickness of 110 nm is formed by the plasmaCVD method. Of course, the gate insulating film is not limited to thesilicon oxynitride film but an insulating film containing other siliconmay be used as a single layer or as a laminated layer.

Further, when a silicon oxide film is used, it is formed by mixing TEOS(Tetraethyl Orthosilicate) and O₂ by plasma CVD method, (which isdischarged) while discharging electric power under a condition withreaction pressure of 40 Pa, a substrate temperature of 300 to 400° C.and high frequency (13.56 MHz) power density of 0.5 to 0.8 W/cm².Thermal annealing at 400 to 500° C. can give good characteristics to thesilicon oxide film formed in this way as a gate insulating film.

Next, a first conductive film 5013, which is 20 to 100 nm in thickness,and a second conductive film 5014, which is 100 to 400 nm in thickness,are stacked on the gate insulating film 5012. In this embodiment, thefirst conductive film 5013 formed by a TaN film with a thickness of 30nm and the second conductive film 5014 formed by a W film with athickness of 370 nm are stacked. The TaN film is formed by sputteringand by using Ta target to perform sputtering in an atmosphere containingnitrogen. The W film is formed by a sputtering using W target.Alternatively, it can be formed by thermal CVD method using tungstenhexafluoride (WF₆). In both cases, the use of the gate electrode needslow resistance. Therefore, the resistivity of the W film is desirably 20μΩcm or less. The low resistance of the W film can be achieved byincreasing the size of the crystal grains. However, when the W filmcontains a large amount of impurity element such as oxygen, thecrystallization is inhibited, which raises the resistance. Accordingly,in this embodiment, the W film is formed by the sputtering using highpurity (purity of 99.9999%) W target and by taking the prevention ofintrusion of impurity from a vapor phase during the film forming intospecial consideration. Thus, the resistivity of 9 to 20 μΩcm can beachieved.

While, in this embodiment, the first conductive layer 5013 is TaN andthe second conductive layer 5014 is W, they are not limited inparticular. Both of them can be formed by an element selected from Ta,W, Ti, Mo, Al, Cu, Cr and Nd or an alloy material or a compound materialmainly containing the above-described element. Alternatively, asemiconductor film, such as representatively a polycrystalline siliconfilm to which an impurity element such as phosphorus is doped, can beused. An AgPdCu alloy may be used. A combination of the first conductivefilm formed by a tantalum (Ta) film and the second conductive filmformed by a W film, a combination of the first conductive film formed bya titan nitride (TiN) film and the second conductive film formed by a Wfilm, a combination of the first conductive film formed by a tantalumnitride (TaN) film and the second conductive film formed by a W film, acombination of the first conductive film formed by a tantalum nitride(TaN) film and the second conductive film formed by an Al film, or acombination of the first conductive film formed by a tantalum nitride(TaN) film and the second conductive film formed by a Cu film ispossible.

Further, the present invention is not limited to a two-layer structure.For example, a three-layer structure may be adopted in which a tungstenfilm, an alloy film of aluminum and silicon (Al—Si), and a titaniumnitride film are sequentially laminated. Moreover, in case of athree-layer structure, tungsten nitride may be used in place oftungsten, an alloy film of aluminum and titanium (Al—Ti) may be used inplace of the alloy film of aluminum and silicon (Al—Si), and a titaniumfilm may be used in place of the titanium nitride film.

Note that, it is important that appropriate etching method or kinds ofetchant is properly selected depending on the materials of a conductivefilm (FIG. 19E).

Next, mask 5015 containing resist using photolithography method areformed, and third etching processing is performed in order to formelectrodes and wires. The third etching processing is performed underfirst and second etching conditions (FIG. 19F). The first etchingcondition in this embodiment is to use Inductively Coupled Plasma (ICP)etching method and to use CF₄, Cl₂ and O₂ as an etching gas, whose gasflow rate ratio is 25:25:10 sccm, respectively. 500 W of RF (13.56 MHz)power was supplied to a coil type electrode by 1 Pa pressure in order togenerate plasma and then to perform etching. 150 W of RF (13.56 MHz)power was also supplied to a substrate side (test sample stage) andsubstantially negative self-bias voltage was applied. The W film wasetched under the first etching condition so as to obtain the end of thefirst conductive layer in a tapered form.

After that, the first etching condition is shifted to the second etchingcondition without removing the mask 5015 containing resist. Then, CF₄and Cl₂ are used as etching gases. The gas flow rate ratio thereof is30:30 sccm. 500 W of RF (13.56 MHz) power is supplied to a coil typeelectrode by 1 Pa pressure in order to generate plasma and then toperform etching for about 30 seconds. 20 W of RF (13.56 MHz) power isalso supplied to a substrate side (test sample stage) and substantiallynegative self-bias voltage is applied. Under the second etchingcondition where CF₄ and Cl₂ are mixed, both W film and TaN film areetched to the same degree. In order to etch without leaving a residue onthe gate insulating film, the etching time may be increased at a rate ofabout 10 to 20%.

In the third etching processing, when the shape of the mask containingresist is appropriate, the ends of the first and the second conductivelayers are in the tapered form due to the effect of the bias voltageapplied to the substrate side. The angle of the tapered portion is 15 to45°. Thus, conductive layers 5016 to 5020 in a first form are formedwhich include the first conductive layers and the second conductivelayers (first conductive layers 5016 a to 5020 a and second conductivelayer 5016 b to 5020 b) through the third etching processing. In a gateinsulating film 5012, an area not covered by the conductive layers 5016to 5020 in the first form is etched about 20 to 50 nm so as to form athinner area.

Next, fourth etching processing is performed without removing mask 5015made from resist (FIG. 20A). Here, CF₄, Cl₂ and O₂ are used as anetching gas to etch the W film selectively. Then, second conductivelayers 5021 b to 5025 b are formed by the fourth etching process. On theother hand, the first conductive layers 5016 a to 5020 a are hardlyetched, and conductive layers 5021 to 5025 in the second form areformed.

First doping processing is performed without removing mask 5015containing resist and low density of impurity element, which givesn-type to the second island-like semiconductor layer, is added. Thedoping processing may be performed by the ion-doping method or theion-implanting method. The ion doping method is performed under acondition in the dose of 1×10¹³ to 5×10¹⁴ atoms/cm² and the acceleratingvoltage of 40 to 80 keV. In this embodiment, the ion doping method isperformed under a condition in the dose of 1.5×10¹³ atoms /cm² and theaccelerating voltage of 60 keV. The n-type doping impurity element maybe Group 15 elements, typically phosphorus (P) or arsenic (As). Here,phosphorus (P) is used. In this case, the conductive layers 5021 to 5025function as masks for the n-type doping impurity element. Therefore,impurity areas 5026 to 5029 are formed in the self-alignment manner. Ann-type doping impurity element in the density range of 1×10¹⁸ to 1×10²⁰atoms/cm³ are added to the impurity areas 5026 to 5029.

When mask 5015 made from resist is removed, new mask 5030 made fromresist is formed. Then, second doping processing is performed by usinghigher accelerating voltage than that used in the first dopingprocessing. The ion doping method is performed under a condition in thedose of 1×10¹³ to 1×10¹⁵ atoms/cm² and the accelerating voltage of 60 to120 keV. In the doping processing, the second conductive layers 5021 bto 5025 b are used as masks against the impurity element. Doping isperformed such that the impurity element can be added to the secondisland-like semiconductor layer at the bottom of the tapered portion ofthe first conductive layer. Then, third doping processing is performedby having lower accelerating voltage than that in the second dopingprocessing to obtain a condition shown in FIG. 20B. The ion dopingmethod is performed under a condition in the dose of 1×10¹⁵ to 1×10¹⁷atoms/cm² and the accelerating voltage of 50 to 100 keV. Through thesecond doping processing and the third doping processing, an n-typedoping impurity element in the density range of 1×10¹⁸ to 5×10¹⁹atoms/cm³ is added to the low density impurity areas 5031 and 5032,which overlap with the first conductive layer. An n-type doping impurityelement in the density range of 1×10¹⁹ to 5×10²¹ atoms/cm³ is added tothe high density impurity areas 5034 to 5036.

With proper accelerating voltage, the low density impurity area and thehigh density impurity area can be formed by performing the second dopingprocessing and the third doping processing once.

Next, after removing mask 5030 made from resist, new mask 5037containing resist is formed and then the fourth doping processing isperformed. Through the fourth doping processing, impurity areas 5038 and5039, to which an impurity element doping a conductive type opposite tothe one conductive type is added, in a second island-like semiconductorlayer, which is an active layer of a p-channel type TFT, are formed.Second conductive layers 5021 a to 5025 a are used as mask against theimpurity element, and the impurity element giving p-type is added so asto form impurity areas in the self-alignment manner. In this embodiment,the impurity areas 5038 and 5039 are formed by applying ion-dopingmethod using diborane (B₂H₆) (FIG. 20C). During the fourth dopingprocessing, the second island-like semiconductor layer forming then-channel TFT is covered by mask 5037 made from resist. Thorough thefirst to the third doping processing, phosphorus of different densitiesis added to each of the impurity areas 5038 and 5039. Doping processingis performed such that the density of p-type doping impurity element canbe 1×10¹⁹ to 5×10²¹ atoms/cm³ in both areas. Thus, no problems arecaused when they function as the source region and the drain region ofthe p-channel TFT.

Impurity areas are formed in the second island-like semiconductorlayers, respectively, through the processes above.

Next, the mask 5037 made from resist is removed and a first interlayerinsulating film 5040 is formed. The first interlayer insulating film5040 may be an insulating film with a thickness of 100 to 200 nmcontaining silicon, which is formed by plasma CVD or sputtering. In thisembodiment, silicon oxynitride film with a thickness of 150 nm is formedby plasma CVD. The first interlayer insulating film 5040 is not limitedto the silicon oxynitride film but may be another insulating filmcontaining silicon in a single layer or in a laminated.

Next, a process for activating impurities added to the secondisland-like semiconductor layer is conducted (FIG. 20D). A laserannealing method is used for the activation process. When a laserannealing method is used, the laser used in the crystallization can beused. When the activation processing is performed, the moving speed isthe same as that of the crystallization, and an energy density of about0.01 to 100 MW/cm² (preferably, 0.01 to 10 MW/cm²) is required. Also, acontinuous oscillation laser may be used in the case the crystallizationis performed and a pulse oscillation laser may be used in the case theactivation is performed.

Also, the activation process may be conducted before the firstinterlayer insulating film is formed.

After the heating processing (thermal processing at 300 to 550° C. for 1to 12 hours) is performed, hydrogenation can be performed. This processterminates the dangling bond of the second island-like semiconductorlayer with hydrogen contained in the first interlayer insulating film5040. The second island-like semiconductor layer can be hydrogenated,irrespective of the existence of the first interlayer insulating film.Alternatively, the hydrogenation may be plasma hydrogenation (usinghydrogen excited by plasma) or heating processing in an atmospherecontaining 3 to 100% of hydrogen at 300 to 650° C. for 1 to 12 hours.

Next, a second interlayer insulating film 5041 formed by an inorganicinsulating material or an organic insulator material is formed on thefirst interlayer insulating film 5040. In this embodiment, an acrylicresin film with a thickness of 1.6 μm is formed. Next, after the secondinterlayer insulating film 5041 is formed, the third interlayerinsulating film 5042 is formed to contact with the second interlayerinsulating film 5041.

Wirings 5043 to 5047 are formed. These wirings are formed by patterninga film laminating a Ti film with a thickness of 50 nm and an alloy film(alloy film of Al and Ti) with a thickness of 500 nm. It is not limitedto the two-layer structure but may be a one-layer structure or alaminate structure including three or more layers. The materials of thewirings are not limited to Al and Ti. For example, the wiring can beformed by forming Al or Cu on a TaN film and then by patterning thelaminate film in which a Ti film is formed (FIG. 20E).

In this way, the drive circuit having a CMOS circuit including ann-channel TFT and a p-channel TFT, and the pixel portion having thepixel TFT and the storage capacitor can be formed on the same substrate.Thus, an active matrix substrate is completed.

The present embodiment can be implemented by freely combining EmbodimentModes 1 to 3 and Embodiments 1 to 6.

Embodiment 8

This embodiment explains, below, a process to manufacture a reflectiontype liquid crystal display device from the active matrix substrate madein Embodiment 7, using FIGS. 20 and 21.

First, after obtaining an active matrix substrate in the state of FIG.20E according to Embodiment 5, an orientation film 5055 is formed atleast on the wiring (the pixel electrodes) 5047 on the active matrixsubstrate and subjected to a rubbing process. Incidentally, in thisembodiment, prior to forming an orientation film 5055, an organic resinfilm such as an acryl resin film is patterned to form columnar spacers5054 in a desired position to support the substrates with spacing.Meanwhile, spherical spacers, in place of the columnar spacers, may bedistributed over the entire surface of the substrate.

Then, a counter substrate 5048 is prepared. Then, coloring layers (colorfilters) 5049, 5050 (though only two color filters are shown here,actually three color filters; R, G, B may be used) and a planarizingfilm 5051 are formed on a counter substrate 5048. A light shieldingportion is formed by overlapping a red color filter 5049 and a bluecolor filter 5050 together. Meanwhile, the light shielding portion maybe formed by partly overlapping a red color filter and a green colorfilter. Similarly, a space between the adjacent pixels is shielded bythe lamination of filters. Thus, description of a process of fabricatingthe light shielding film is omitted.

Then, a counter electrode 5052 of a transparent conductive film isformed on the planarizing film 5051 at least in the pixel portion. Anorientation film 5053 is formed over the entire surface of the countersubstrate and subjected to a rubbing process.

Then, the active matrix substrate and the counter substrate are bondedtogether by a seal member (not shown). The seal member (not shown) ismixed with filler so that the filler and the columnar spacers bondtogether the two substrates with an even spacing. Thereafter, a liquidcrystal material 5056 is poured between the both substrates, andcompletely sealed by a sealant (not shown). The liquid crystal material5056 may be a known liquid crystal material. In this manner, completedis a reflection type liquid crystal display device shown in FIG. 21. Ifnecessary, the active matrix substrate or counter substrate is dividedinto a desired shape. Furthermore, a polarizing plate (not shown) isbonded only on the counter substrate. Then, an FPC (Flexible PrintCircuit) substrate is bonded by a known technique.

The liquid crystal display device manufactured by the above processincludes a TFT formed by using a semiconductor film in which crystalgrains with large grain sizes are formed by irradiating a laser lightwith periodic or uniform energy density thereon and the operatingcharacteristic and the reliability of the above-mentioned liquid crystaldisplay device can be enough. Further, such a liquid crystal displaydevice can be used as a display portion of all kinds of electronicdevices.

The present embodiment can be implemented by freely combining withEmbodiment Modes 1 to 3 and Embodiments 1 to 7.

Embodiment 9

In this embodiment, an example of a method for manufacturing a lightemitting device will be described. The manufacturing method uses anactive matrix substrate manufactured using the manufacturing method forthe active matrix substrate described in Embodiment 7. The “lightemitting device” is a generic name of a display panel formed such thatlight-emitting elements formed on a substrate are hermetically enclosedinto between the substrate and a cover material, and a display module inwhich TFTs and the like are mounted on the display panel. Thelight-emitting element includes a layer (light-emitting layer)containing an organic compound with which electroluminescence (ElectroLuminescence) generated by an electric field being applied is obtained,an anode layer, and a cathode layer. The electroluminescence in theorganic compound has a luminescence (fluorescence) generated when thestate returns from a single excited state to a normal state and aluminescence (phosphorescence) generated when the state returns from atriplet excited state to a normal state. The organic compound of thisembodiment includes either one of these two types or the both types.

In the present specification, all layers formed between the anode andthe cathode in the light-emitting element are defined as EL layers.Specifically, the EL layers include a light-emitting layer, a holeinjection layer, an electron injection layer, a hole transporting layer,an electron transporting layer and the like. Basically, thelight-emitting element has a structure in which an anode layer, alight-emitting layer, and a cathode layer are overlaid in that order. Inaddition to the structure, the light-emitting layer has a structure inwhich, an anode layer, a hole injection layer, a light-emitting layer,and a cathode layer are overlaid in that order or an anode layer, a holeinjection layer, a light-emitting layer, an electron transporting layer,and a cathode layer are overlaid in that order.

After the formation of layers up to a third interlayer insulating film5102 according to Embodiment 7, the pixel electrode working as the anodeof the light-emitting element is formed of a material that is atransparent conductive film. To form the transparent conductive film,there can be used any one of a compound of indium oxide and tin oxide, acompound of indium oxide and zinc oxide, zinc oxide, tin oxide, andindium oxide. Alternatively, a transparent conductive film containinggallium may be used for the transparent film.

In the case of the light emitting device, the third interlayerinsulating film 5102 is effective to prevent intrusion of moisturecontained in the second interlayer insulating film 5101 into the organiclight-emitting layer. When the second interlayer insulating film 5101contains an organic resin material, since the organic resin materialcontains much moisture, the provision of the third interlayer insulatingfilm 5102 is significantly effective. In addition, in this embodiment,it is very important to level stepped portions formed with TFTs by usingthe second interlayer insulating film 5101 formed from the resin. Sincethe light-emitting layer to be formed in a later step is very thin,defects in light emission can occur because of the existence of thesteps. For this reason, the stepped portions are desirably leveledbefore the formation of the pixel electrode so that the light-emittinglayer can be formed on a surface leveled as flat as possible.

The n-channel TFT and the p-channel TFT contained in the drive circuitare formed using the manufacturing method described in Embodiment 5. Inthis embodiment, while the TFTs have a single-gate structure, the TFTsmay have a double-gate structure or a triple-gate structure.

Subsequently, as shown in FIG. 22B, a resin film formed of diffusedmaterials, such as a black dye, carbon, and black pigment, is formed insuch a manner as to cover the third interlayer insulating film 5102, anopening is formed in a portion to be a light emitting element and ashielding film (not shown) is thus formed. As the resin, representativeexamples include, for example, polyimide, polyamide, acrylic resin,benzocyclopolybutene (BCB) etc.; however, the material is not limitedthereto. A material other than the organic resin may also be used as amaterial of the shielding film, of which examples are materials made bymixing a black dye, carbon, or black pigment with silicon, siliconoxide, silicon oxynitride, or the like. The shielding film is effectiveto prevent outside light reflected on wirings 5104 to 5110 from beingvisible to a viewer. After the above-described processing, contact holesreaching the individual impurity regions are formed, and the wirings5104 to 5110 are then formed.

Subsequently, a bank 5111 is formed of a resin material. The bank 5111is formed such that an acrylic film or polyimide film having a thicknessof 1 to 2 μm is patterned to allow a pixel electrode 5103 to partly beexposed.

An EL layer 5112 is formed over the pixel electrode 5103. While FIG. 22Bshows only one pixel, EL layers are separately formed corresponding tothe individual colors R (red), G (green), and B (blue) in thisembodiment. In addition, in this embodiment, a low-molecular basedorganic light-emitting material is formed by an evaporation method.Specifically, the material is formed to be a multi-layered structuresuch that a 20-nm thick copper phthalocyanine (CuPc) film is provided asa hole injection layer, and a 70-nm thick tris-8-hydroxyquinolinatoaluminum complex (Alq₃) film is formed thereon as a light-emittinglayer. The luminescent color can be controlled by adding a fluorescentpigment, such as quinacridone, perylene, or DCM1, to Alq₃.

However, the above examples are simply an example of organiclight-emitting materials which can be used as the light-emitting film,and the present invention is not limited thereto in any way. Thelight-emitting layer (layer for causing light emission and a carrierthereof to move) may be formed by arbitrarily combining light-emittinglayers and charge transporting films (or, charge injection layers). Forexample, while this embodiment has been described with reference to theexample in which the low-molecular based organic light-emitting materialis used as the light-emitting material, either intermediate-molecularbased organic light-emitting material or a high-molecular based organiclight-emitting material may be used. In this case, theintermediate-molecular based organic light-emitting material refers toan organic light-emitting material that does not have sublimationcharacteristics and that has 20 or fewer molecules or has a chainedmolecule length of 10 μm or smaller. As an example use of thehigh-molecular based organic light-emitting material, a multi-layeredstructure may be formed such that a 20-nm polythiophene (PEDOT) film isprovided by spin coating as a hole injection film, and a polyphenylenevinylene (PPV) film of about 100 nm is provided thereon as alight-emitting film. Meanwhile, when π-conjugate based high molecules ofPPV are used, light-emission wavelengths for a color range of from redto blue become selectable. Moreover, an inorganic material such assilicon carbide may be used as a material of the charge transportingfilm or the charge injection layer. For these organic light-emittingmaterials and inorganic materials, known materials may be used.

Next, a pixel electrode 5113 is provided as a cathode on the EL layer5112. In this embodiment, an (aluminium) aluminum-lithium alloy film isused as the conductive film. (As a matter) of course, a known MgAg film(magnesium-silver alloy film) may be used. For the material of thecathode, either a conductive film formed of elements belonging to Group1 or 2 in the periodic table or a conductive film to which thesematerials are added may be used.

The light-emitting element is completed upon formation of the layers upto the pixel electrode 5113. In this case, the light-emitting elementrefers to an element formed of the pixel electrode 5103 (anode), the ELlayer 5112, and the cathode 5113.

In addition, a protection film 5114 may be formed in such a manner as tofully cover the light-emitting element. The protection film 5114 isformed of an insulating film including a carbon layer, a silicon nitridefilm, or a silicon oxynitride film, in which the insulating film is usedin the form of either a single layer or a combined multilayer.

In this case, a film having a good coverage is preferably used for theprotection film 5114; specifically, using a carbon film, particularly, aDLC (diamond-like carbon) film is effective. Since the DLC film can beformed in a temperature range of from a room temperature to 100° C. orlower, the film can easily be formed also on an upper portion of thelight-emitting layer 5112 having a low heat resistance. In addition,since the DLC film has a high blocking effect against oxygen,oxidization of the light-emitting layer 5112 can be suppressed.Therefore, this enables to prevent a problem of oxidizing thelight-emitting layer 5112 from occurring while a subsequent sealing stepis being performed.

As described above, according to this embodiment, all the light-emittinglayers 5112 are covered by the inorganic insulating film that has a highbarrier property and that is formed of, for example, carbon, siliconnitride, silicon oxynitride, aluminum nitride, aluminum oxynitride orthe like. Accordingly, the light-emitting layer can be prevented evenmore efficiently from being deteriorated due to entrance of moisture,oxygen, and the like.

In addition, when a silicon nitride film formed by a silicon-targetedsputtering is used for the third interlayer insulating film 5102 and theprotection film 5114, entrance of impurity into the light-emitting layercan be prevented even more efficiently. While film formation conditionsmay appropriately be selected, sputtering is preferably performed usinga nitrogen (N₂) or nitrogen-argon mixture gas and applying a highfrequency power. In this case, the substrate temperature may bemaintained at a room temperature, and no heating means needs to be used.When an organic insulating film or an organic compound layer has alreadybeen formed, the film formation is desirably performed with thesubstrate not being heated. However, in order to completely removeabsorbed or occluded moisture, dehydration processing is preferablyperformed by heating the object for a period of several minutes toseveral hours at a temperature of 50 to 100° C. in a vacuum.

It is known that when a silicon nitride film is formed according to asputtering performed in such a manner that silicon is targeted in a roomtemperature, a high frequency power of 13.56 MHz is applied, and only anitrogen gas is used, the silicon nitride film is characterized asdescribed hereunder. That is, in infrared adsorption spectra thereof,adsorption peaks of an N—H connection and an Si—H connection are notobserved, nor is an adsorption peak of an Si—O. In addition, the oxygenconcentration and the hydrogen concentration in the film are not higherthan 1 atom %. Also from the above, it can be known that entrance ofimpurity such as oxygen and moisture can be prevented even moreefficiently.

In this manner, the light-emitting device having the structure as shownin FIG. 22B is completed. Note that, it is effective that the steps upto the formation of the protection film 5114 after the formation of thebank 5111 are not exposed to the atmosphere but are continuallyprocessed.

In this embodiment, while the shielding film is formed between the thirdinterlayer insulating film 5102 and the bank 5111, the present inventionis not limited thereto. It is essential that the shielding film beprovided in a position where outside light reflected in the wirings 5104to 5110 is prevented from being visible to a viewer. For example, as inthis embodiment, in the configuration where light emitted from thelight-emitting element is directed to the substrate, the shielding filmmay be provided between the first interlayer insulating film and thesecond interlayer insulating film 5101. Also in this case, the shieldingfilm includes an opening to enable the light from the light-emittingelement to pass.

In addition, as described in Embodiment 7, the provision of the impurityregion overlapping the gate electrode via the insulating film enablesthe formation of the n-channel TFT that has high resistance againstdeterioration occurring due to hot carrier effects. Accordingly, thelight emitting device having high reliability can be implemented.

In this embodiment, only the configurations of the pixel portion and thedrive circuit have been described. However, according to themanufacturing steps of this embodiment, other logic circuits such as asignal dividing circuit, a D/A converter, an operational amplifier, andγ correction circuit, can be formed on the same insulating material.Further, a memory, a microprocessor, and the like can also be formed.

The light emitting device manufactured as described above can be suchthat laser light of which energy distributions are periodic and uniformis irradiated, that includes TFTs manufactured using semiconductorlayers in which large-size crystal grains are formed, and that exhibitssufficient performance characteristics and reliability. The lightemitting device of the type described above can be used as displayportions of various electronic devices.

According to this embodiment, light emitted from the light-emittingelement is directed to the TFT. However, the light may be directed tothe opposite side of the TFT. In this case, a resin mixed with a blackdye, carbon, or black pigment may be used for the bank 5111. In thiscase, a material having high reflectance is used for the pixel electrode5103, and a transparent conductive film is used for the pixel electrode5113.

This embodiment may be implemented by freely combining with EmbodimentModes 1 to 3 and Embodiments 1 to 8.

Embodiment 10

In this embodiment, the cross-sectional structure of a TFT formed usingthe preparation method of the present invention will be described.Particularly in this embodiment, the cross-sectional structure of abottom-gate-type TFT formed using the preparation method utilizing theprinciple of grapho-epitaxy will be described.

The description refers to FIG. 25. As shown in FIG. 25A, a first basefilm 1402 a is formed on a substrate 1400. After that, a second basefilm is formed and patterned to form a protruding part 1402 b.

As the first base film 1402 a and the second base film, silicon oxide,silicon nitride-oxide, silicon oxynitride or the like can be used.However, in consideration of the step of patterning only the second basefilm formed on the first base film 1402 a to form the protruding part1402 b, the first base film 1402 a and the second base film need tocontain different materials. Thus, the first base film 1402 a and theprotruding part 1402 b form a recessed and protruding pattern.

Next, as shown in FIG. 25B, a conductive film is patterned to form agate electrode 1403. It is desired that an end part of the gateelectrode 1403 is tapered. Thus, a film formed on the top of the gateelectrode 1403 can be prevented from being interrupted by steps. Afterthat, a gate insulating film 1404 is formed. A semiconductor film 1405is formed thereon. The semiconductor film 1405 is laser-annealed andthus crystallized. In laser annealing, a continuously oscillating laserbeam is used. A beam spot formed by condensing this laser beam is movedon the semiconductor film. The semiconductor film is thus crystallized.

A designer can properly decide the shape and scanning direction of thebeam spot in accordance with the shape of the recessed and protrudingpattern.

Next, as shown in FIG. 25C, the crystallized semiconductor film 1405 ispatterned to form an island-like semiconductor 1406. A channel stopper1407 is formed thereon.

Next, as shown in FIG. 25D, doping with impurity elements is carried outthrough the channel stopper 1407. In this manner, a channel region 1408overlapping the gate electrode 1403, and impurity regions 1409 a and1409 b functioning as a source region and a drain region are formed.

Then, as shown in FIG. 25E, an interlayer insulating film 1410 isformed. Next, contact holes reaching the impurity regions 1409 a and1409 b are formed. After that, a conductive film is deposited andpatterned into a predetermined shape, thus forming a terminal 1411 a anda terminal 1411 b. One of the terminals 1411 a and 1411 b is equivalentto a source terminal. The other is equivalent to a drain terminal.

In the TFT thus formed, a polycrystalline semiconductor film formed onthe protruding part of the recessed and protruding pattern is used as achannel region. Thus, the TFT having the channel region with goodcrystallinity can be manufactured.

This embodiment can be freely combined with Embodiment Modes 1 to 3 andEmbodiments 1 to 9.

Embodiment 11

In this embodiment, the cross-sectional structure of a TFT formed usingthe preparation method of the present invention will be described.Particularly in this embodiment, the cross-sectional structure of a TFThaving sidewalls and formed using the preparation method utilizing theprinciple of grapho-epitaxy will be described.

In FIG. 26A, an base film 1501 and an base film 1502 are formed on asubstrate 1500 having an insulating surface. On the base film 1502, anactive layer is provided which includes a channel forming region 1505,first impurity regions 1504 sandwiching the channel forming region 1505,and second impurity regions 1503 sandwiching the first impurity regions1504 and the channel forming region 1505. A gate insulating film 1506contacting the active layer, and a gate electrode 1508 formed on thegate insulating film 1506 are provided. Sidewalls 1507 are formed incontact with the lateral sides of the gate electrode 1508.

The sidewalls 1507 are superimposed on the first impurity regions 1504with the gate insulating film 1506 provided between them. The sidewalls1507 may be electrically conductive or insulating. If the sidewalls 1507are electrically conductive, the sidewalls 1507 may be considered to bea part of the gate electrode.

In FIG. 26B, an base film 1511 and an base film 1512 are formed on asubstrate 1510 having an insulating surface. On the base film 1512, anactive layer is provided which includes a channel forming region 1515,first impurity regions 1514 sandwiching the channel forming region 1515,and second impurity regions 1513 sandwiching the first impurity regions1514 and the channel forming region 1515. A gate insulating film 1516contacting the active layer, and a gate electrode made up of two layersof conductive films 1519 and 1518 stacked on the gate insulating film1516 are provided. Sidewalls 1517 are formed in contact with the topsurface of the conductive film 1519 and the lateral sides of theconductive film 1518.

The sidewalls 1517 may be electrically conductive or insulating. If thesidewalls 1517 are electrically conductive, the sidewalls 1517 may beconsidered to be a part of the gate electrode.

In FIG. 26C, an base film 1521 and an base film 1522 are formed on asubstrate 1520 having an insulating surface. On the base film 1522, anactive layer is provided which includes a channel forming region 1525,first impurity regions 1524 sandwiching the channel forming region 1525,and second impurity regions 1523 sandwiching the first impurity regions1524 and the channel forming region 1525. A gate insulating film 1526contacting the active layer is formed, and then a conductive film 1528,a conductive film 1529 covering the top surface and the side surfaces ofthe conductive film 1528, and sidewalls 1527 contacting the lateralsides of the conductive film 1529 are formed on the gate insulating film1526. The conductive film 1528 and the conductive film 1529 function asa gate electrode.

The sidewalls 1527 may be electrically conductive or insulating. If thesidewalls 1527 are electrically conductive, the sidewalls 1527 may beconsidered to be a part of the gate electrode.

This embodiment can be freely combined with Embodiment Modes 1 to 3 andEmbodiments 1 to 9.

EFFECT OF THE INVENTION

The present invention provides a method for preparing a semiconductor inwhich plural second island-like semiconductors constituting a unitcircuit are formed from first island-like semiconductors that aredifferent from each other. For example, in the case of forming a unitcircuit using three second island-like semiconductors, the three secondisland-like semiconductors are set to be at different distances from apointed end part (a-point). Thus, the different properties of the secondisland-like semiconductors can be averaged. As a result, the propertiesof unit circuits can be equalized.

1. A method for manufacturing a semiconductor device comprising: formingan insulating film having plural projections over a substrate; forming afirst film comprising amorphous semiconductor over the insulating filmand at least between the projections; heating the first film forimproving crystallinity of the first film comprising amorphoussemiconductor, thereby producing a second film comprising crystallinesemiconductor; etching the second film comprising crystallinesemiconductor, thereby forming plural third films comprising crystallinesemiconductor; irradiating the plural third film comprising crystallinesemiconductor with a laser beam having a linear shape with changing aposition of the substrate relative to the laser beam for improvingcrystallinity of the plural third films, thereby producing a pluralfourth films comprising crystalline semiconductor; etching the pluralfourth films comprising crystalline semiconductor for forming pluralfifth films comprising crystalline semiconductor from the plural fourthfilms; and forming a circuit comprising plural transistors from at leasta part of the plural fifth films comprising crystalline semiconductor,wherein at least the part of the fifth films are obtained from at leasttwo of the fourth films.
 2. A method of manufacturing a semiconductordevice according to claim 1, further comprising forming a layercontaining a metal element over the first film comprising amorphoussemiconductor before heating the first film.
 3. The method formanufacturing a semiconductor device according to claim 1, wherein theplural transistors are arranged so that all directions of migration ofelectric charges in their channel forming regions are substantiallyparallel to each other.
 4. The method for manufacturing a semiconductordevice according to claim 1, wherein directions of migration of electriccharges in channel forming regions of the plural transistors areparallel to the direction of changing a position of the substraterelative to the laser beam.
 5. The method for manufacturing asemiconductor device according to claim 1, wherein the pluraltransistors are connected in parallel.
 6. The method for manufacturing asemiconductor device according to claim 1, wherein the laser beam isoscillated from a continuous wave laser apparatus.
 7. The method formanufacturing a semiconductor device according to claim 1, wherein thelaser beam is oscillated from a continuous wave laser selected from aYAG laser, a YVO₄ laser, a YLF laser, a YAlO₃ laser, a glass laser, aruby laser, an alexandrite laser, and a Ti:sapphire laser.
 8. The methodfor manufacturing a semiconductor device according to claim 1, whereinthe laser beam is oscillated from a laser selected from a continuouswave excimer laser, an Ar laser, a Kr laser, and a CO₂ laser.
 9. Themethod for manufacturing a semiconductor device according to claim 1,wherein the laser beam is oscillated from a laser selected from acontinuous wave helium cadmium laser, a copper vapor laser, and a goldvapor laser.